This disclosure relates to a method for producing and using catalysts for the production of bisphenols, and in particular to a method for producing catalysts which contain attached poly-sulfur mercaptan promoters, and using these catalysts in the production of bisphenol-A, and its derivatives.
Typical bisphenols, such as 4,4′-isopropylidenediphenol, e.g., bisphenol-A (BPA), are widely employed as monomers in the manufacture of polymeric materials, such as engineering thermoplastics. For example, BPA is a principal monomer used in the manufacture of polycarbonate. Bisphenols are generally prepared by the electrophilic addition of aldehydes, or ketones such as acetone, to aromatic hydroxy compounds such as phenol, in the presence of an acidic catalyst compositions. These types of reactions are also referred to as acid catalyzed condensation reactions. Commercially, sulfonated polystyrene resin cross-linked with divinylbenzene, e.g., PS-DVB, is typically used as a solid acid component of the catalyst composition. Reaction promoters can also be employed as part of a catalyst composition to improve the reaction rate, and selectivity, of the desired condensation reaction; in the case of BPA, the desired selectivity is for the para-para isomer (pp-BPA). Promoters can be present as unattached molecules in the bulk reaction matrix, e.g., “bulk-promoters”, or can be attached to the resin through ionic linkages, e.g., “attached-promoters”. A useful class of promoter is the mercaptans, specifically thiols, e.g., organosulfur compounds which are derivatives of hydrogen sulfide. Typical mercaptan promoters contain only a single sulfur atom, and result in catalyst compositions that catalyze bisphenol formation with poor isomer selectivity; in the case of BPA, the undesired selectivity if for the ortho-para isomer (op-BPA). Consequently, a long felt yet unsatisfied need exists for new and improved catalyst compositions, and a method to produce them, which are selective in the production of bisphenols. Herein, a method to produce catalyst compositions comprising poly-sulfur mercaptan promoters is disclosed. The use of poly-sulfur mercaptan promoters results in catalyst compositions that are highly selective in the formation of bisphenols.